The effect of varying the number of contributors in the prosecution and alternate propositions

• NCJ Number: 254181
• Author(s): John. S. Buckleton; Jo-Anne Bright; Kevin Cheng; Hannah Kelly; Duncan A. Taylor
• Date Published: January 2019
• Length: 7 pages
• Grant Number(s): 2017-DN-BX-K541
• Agencies: NIJ-Sponsored
• Publication Type: Research (Applied/Empirical); Report (Study/Research); Report (Grant Sponsored); Program/Project Description

Annotation

Using a simplified model, this study examined the effect of varying the number of contributors in the prosecution and alternate propositions for a number of simulated examples.

Abstract

The study compared the Slooten and Caliebe solution with several existing practices. The authors own experience is that most laboratories, including their own, assign the number of contributors, by allele count and a manual examination of peak heights. The LRn for one or a very few values is calculated and typically one of these is presented, usually the most conservative. This gives an acceptable approximation. Reassessing the number of contributors if LR=0 and adding one to N under both Hp and Ha to "fit" the POI may lead to a substantial overstatement of the LR. A more reasonable option is to allow optimization of the assignment under Hp and Ha separately. The authors show that an additional contributor explained the single locus profile better when PHR is greater than or equal to 0.51. This is in line with current interpretation approaches. Collectively. these trials and the solid theoretical development suggest that the Slooten and Caliebe approach performs well. (publisher abstract modified)